Conventionally, a new transportation system in which a vehicle runs on a predetermined track by rotating rubber tire wheels carrying the vehicle body, incorporates, in general, a steering unit for turning the rubber tire wheels serving as running wheels along a predetermined track, different from a rail way vehicle which runs on a railway.
Patent Document 1 (Japanese Utility Model Laid-Open No. 05-8613) discloses a steering unit of the above-mentioned kind in which values of magnetic fields produced from a guide cable laid along a guide path are detected by a pair of left and right magnetic sensors incorporated in a running vehicle so as to compute a value of deviation of the running vehicle from output values therefrom in order to steer the vehicle in a direction in which the value of deviation is decreased, thereby to run the vehicle along the guide path.
However, the steering control with the use of such feed-back control that a value of deviation of a vehicle with respect to the guide cable is computed so as to steer the wheels in a direction in which the value of deviation is decreased, cannot follow up, by itself alone, high speed running at a high speed up to a maximum speed of 80 Km as in the new transportation system, and accordingly, there would be caused a risk incapable of carrying out such fine steering control that the positions of the centers of the axles of the front and rear wheels can follow one and the same locus, that is, a running locus can be set within a predetermined range of left and right displacements.
Further, Patent Document 2 (Japanese Patent Laid-Open No. 2001-243033) discloses a steering control unit for a vehicle, which carries out steering control for a running vehicle without using a desired control value based upon a predetermined course configuration. This steering control unit detects magnetic markers arranged on a course while detecting a running distance of the vehicle, and a position of the vehicle from a GPS or a track-and-vehicle intercommunication or the like, so as to estimate a course along which the vehicle should travel in view of the position of a detected marker position, thereby to carry out the steering control being based upon the thus estimated course.
However, the course estimating means should carry out complicated computation with a long computation time while a curse should be estimated at several positions, there would be caused such a problem that a response speed under control delays. Further, since only the front wheels are steered, such fine control that the positions of the centers of the front and rear wheel axles can substantially follow up one and the seam locus cannot be carried out. Further, the steering control is based upon an equation of vehicle motion in view of a yaw angle. Thus, although the stability can be enhanced, no fine control for allowing the positions of the centers of the front and rear wheel axles to substantially follow one and the same locus would be able to be made even in the case of four wheel steering since both control for the front wheels and control for the rear wheels influence upon each other.
Further, since the discrete detection of track-widthwise positions from the magnetic markers causes acquirement of terms for updating a control instruction value to be discrete, there would be caused such a risk incapable of carrying out fine control for allowing the positions of the front and rear wheel axles to substantially follow up one and the same locus. Should the fine control for allowing the positions of the centers of the front and rear wheel axles to substantially follow up one and the same locus be impossible, the drive comfortability would be deteriorated, and as a result, it is required to increase the width of the track. Thus, there would be caused a problem of increasing construction costs.
The applicant has been previously proposed a track type transportation system for vehicles, in which a vehicle runs on a predetermined track, incorporating a steering unit for automatically steering the front and rear wheels of the vehicle by means of actuators, and a fail-safe mechanism for preventing the vehicle from coming off from the track even though the automatic steering system becomes malfunctioning (refer to Patent Document, Japanese Patent Laid-Open No. 2006-306334). Explanation will be hereinbelow made of the track type transportation system disclosed in the Patent Document 3 with reference to FIGS. 7, 8a and 8b. 
As shown in FIGS. 7, 8a and 8b, the vehicle 012 incorporating the track type transportation system 010 runs along a track 01 which includes a U-like sectional shape protecting track 014 laid at a substantially center of the track 01 and having a channel-like shape with respect to a road surface 015. The U-like sectional shape protecting track 014 is formed by laying a U-like channel steel.
A front wheel bogie 016 and a rear wheel bogie (which is not shown) for carrying the vehicle 012 are provided underneath the vehicle, respectively in the front and rear parts of the vehicle 012. The front wheel bogies 016 is mounted thereto with an axle 044 for front wheels 018, which is therefore pivotable left and right. The front wheels 18 are mounted thereon with core type tires 020. The rear wheel bogie is also mounted thereto with an axle for rear wheels 022 which is not shown and which is pivotable, left and right. The rear wheels 022 are also mounted thereon with core type rubber tires 020, similar to the front wheels 018.
Next, explanation will be made of the steering unit, focusing on the front wheels 018 side. It is noted the configuration on the rear wheels 022 side is similar to that on the front wheel 018 side.
As shown in FIGS. 7, 8a and 8b, there are provided a front steering arm 028a coupled to a front left wheel 018b and extending forward, and a rear steering arm 030a extending rearward. Further, there is provided a rear steering 030b extending rearward and connected to a front right wheel 018a. A tie rod 032 is laid between the rear end parts of the steering arms 030a, 030b for the rear wheels, that is, the steering arms 030a, 030b and the tie rod 032 are rotatably coupled to each other by means of spherical joints 034.
Further, a movable rod 038 from an actuator 036 is rotatably coupled at its one end part to the front end part of the front steering arm 028a by means of a spherical joint 034. The above-mentioned actuator 036 is mounted to the front wheel bogie 016. The actuator 036 may be composed of, for example, a motor and a ball screw mechanism as a specific structure. However, there may be used any means for carrying out translational motion, such as a pneumatic or hydraulic servo cylinder or a linear motor as the actuator.
It is noted that the tie rod 032 and the rear steering arms 030a, 030b constitute the so-called Ackermann-Jeantaud type link mechanism for appropriately controlling a turn angle of the left and right wheels during turning, and further, the left wheel 018 and the light wheel 018a are linked together by the tie rod 032 so as to surely steer the left and right wheels.
Next, explanation will be made of the fail-safe mechanism. The fail safe mechanism 011 is composed of a protection arm 042 mounted thereto with protection wheels 040, and a protection track 014. The protection wheels 042 are cylindrical and are rotatably supported to the lower surface side of the protection arm 042 in the front and rear end parts thereof. Further, the protection wheels 040 are inserted in the U-like protection track 014, and are arranged so that their peripheral surfaces are faced to the left and right walls 014a of the protection track 014. The protection wheels 040 are desirably made of urethane rubber which is highly vibration-resistant and wear-resistant, a material using a steel belt which is used, for example, for a rubber tire, or the like.
Further, the gap between the protection wheel 040 and each side wall 014a of the protection track 014 is smaller than an allowable range in which the vehicle 012 should not be turned left and right further more, and accordingly, the protection wheels 040 do not make contact with the left and right side walls 014a as far as the steering mechanism is normal. The gap between the protecting wheel 040 and the protection track 014 is set in general in a range from 80 to 100 mm.
The protection arm 042 is extended in the longitudinal direction of the vehicle with the center part thereof being rotatably supported to the lower part of the axle 044 of the front wheels 018.
It is noted that the protection wheels has such a height that it may be located above the road surface 015 as shown in FIG. 8a but it may be located below the road surface 015 as shown in FIG. 8b. Thus, there can be selected a structure which can be adapted for the existing running track in view of a replacement specification, that is, more flexible adaptation can be made.
The protection arm 042 is coupled in the vicinity of one end part thereof to the front end part of the front steering arm 028a through the intermediary of a link rod 046. The link rod 046 and the protecting arm 042 are configured so as to direct the protecting wheels 040 in the same direction as the steered direction of the front wheels 018.
The steering mechanism is composed of the actuator 036, the movable rod 038, the front steering am 028a and the rear steering arms 030a, 030b, and the link mechanism is composed of the protection arm 042 and the link rod 046.
Further, the front steering arm 028a is provided in its front end part with a double spherical joint 050 with which one end part of the movable rod 038 of the actuator 036 is coupled to the front end part of the front steering arm 028a in such a condition that they are overlapped one upon another with each other. With the use of the above-mentioned double spherical joint 050, it is possible to effectively use a space.
In the steering mechanism having the above-mentioned configuration, on the basis of a ground position signal (ground position data) and vehicle position data, which are inputted to a control means 082 shown in FIG. 7, the control means 082 delivers a steering instruction signal. Thus, the actuator 036 is operated in response to the steering instruction signal, and accordingly, the actuator 036 applies a steering force to the front left wheel 018b so as to transmit the steering force from the front steering arm 028a to the rear steering arm 030a, and then to the front right wheel 018 by way of the tie rod 032.
Further, the steering force from the actuator 036 is also transmitted from the double spherical joint 050 to the protecting arm 042 by way of the link rod 046, and accordingly, the protection wheels 040 are also moved in association with the motion of the actuator 036 so as to be directed in the same direction as that of the front wheels 018. Thus, the protection wheels 040 are moved together with the running vehicle without making contact with the side walls 014a of the protecting track 014.
When the steering mechanism is malfunctioning, the protecting wheels 040 make contact with the side walls 014a of the protecting track 014. Thereafter, the steering by the actuator 036 is released so as to make the automatic steering mechanism free, and accordingly, the front wheels 018 can be turned in response to the motion of the protection arm 042 along the side walls of the protecting track 014 in order to steer the vehicle 012.
With the configuration of the above-mentioned fail-safe mechanism 011, the vehicle can be safely protected so as to surely transport the passengers even though the automatic steering mechanism fails and so forth, thereby it is possible to ensure a safety and a reliability.
In the steering system disclosed in the Patent Document 3, the front and rear wheels of the vehicle are automatically steered by means of the actuators in order to guide the vehicle so that the vehicle can follow up a desired running locus. However, there would be possibly caused such a problem that the vehicle deviates from a desired locus (specifically, the line connecting between the centers of the axles of the respective front and rear bogies of the vehicle), being caused by disturbance (an initial positional deviation, an inferior running track surface, a shift of the gravitational center of the vehicle, vibration during running, a crosswind, a tire internal pressure, a road surface condition cause by a rain fall).
Thus, in order to precisely determine whether the vehicle follows up a desired running locus or not, it is required to precisely measure a deviated value widthwise of the track.